1. FIELD OF THE INVENTION
This invention relates to an axis changeover apparatus which, when a machine tool having a tool such as a cutter possesses a plurality of axes, controls the changeover of these axes.
2. DESCRIPTION OF THE RELATED ART
When a tool is moved and controlled based on command data from an NC command tape in an automatic lathe which performs turning work by means of a tool such as an ordinary cutter, a stroke limit is set with regard to each axis of movement in such a manner that the tool will not collide with a table or a tool rest.
The same is true for large-scale machine tools having a plurality of axes along the same direction of movement. These include multiple-axis machine tools in which the directions of movement of two axes, such as of a cross rail and quill, coincide with the direction of movement of the tool. In a case where machining is carried out by moving the tool a small amount at a specific portion of a workpiece in such a multiple-axis machine tool, the quill axis is used. When a large amount of movement is made, as when changing a machined portion, the cross rail is used.
In such a machine tool, there are many cases where the mechanical arrangement is such that one axis rides on another. Moreover, it is necessary to set an allowable value for the stroke of movement of each axis. Consequently, depending upon the program of the workpiece to be machined, there are instances in which the amount of movement along an axis of the tool in one machining step becomes too large and exceeds the movable stroke set for a specific axis. For example, when a machining step is programmed in which the movable stroke of the quill is exceeded, machining becomes impossible even if commands are issued. However, irrespective of the fact that the cross rail generally has the same direction as the quill, the commands on the NC tape are created by being divided into commands for the quill axis and commands for the cross rail axis. Hence, commands are formed separately for the cross rail and quill.
Accordingly, not only must the programmer create a command tape while being constantly aware of the allowable stroke set for each axis of the machine tool, but he must also form the commands separately for the cross rail and quill. As a result, only a program conforming to the allowable stroke values can be created. Further, this means that a machine tool in which the strokes of the cross rail and quill differ cannot make use of a program, even if it has the same contents, that has already been created for another machine tool.